As usual, a magnetic shield is realized by perfectly covering an area that is sufficiently larger than a measured area with a high permeability material. However, in this case, in a device that measures magnetism generated from a human body, because a space that is larger than the human body is covered with a high permeability, a large space that is 2 m×2 m×2 m (depth, width, height) is required (for example, Non-Patent Document 1:IEEE Tran. MAG. Vol. MAG-18, No. 1, pp. 260-270, Jan.). A magnetically shielding apparatus obtains a high magnetic shield effect, but suffers from such a problem that a large location space is required, for example, in the case where the magnetically shielding apparatus is located within a hospital, the hospital is limited to a large hospital. Also, since the magnetically shielding apparatus completely constitutes a closed space, there is an adverse effect that the apparatus increasingly makes things psychogenic uncomfortable for a person to be examined.
Under the circumstances, as another method, there has been reported a magnetically shielding apparatus in which circular cylinders which are different in diameter from each other and made of a plurality of high permeability materials are sequentially concentrically arranged, and gaps are defined between the respective adjacent cylinders (Patent Document 1: JP-A No. 214166/1997). The cylinders that are open at both ends thereof and made of the high permeability materials are coaxially combined together, thereby making it possible to solve such a problem that the occupied space is large.
In Patent Document 1, there is a disclosure that a large number of permalloy plates which are made of a high permeability alloy material of Ni—Fe base are used to fabricate a magnetically shielded room such as a prefab room as the conventional art. The conventional art suffers from such a problem that a long time is required for fabrication of the magnetic shield, the number of parts used in the magnetic shield is large, and the magnetic shield becomes very expensive. Patent Document 1 discloses that a rate of the price occupied by the magnetic shield with respect to the price of the biologic magnetic signal measurement apparatus is large, and it is desirable to reduce the costs of the magnetic shield.
Also, there has been reported a technique by which in order to obtain the higher magnetic shield effect within the magnetically shielding apparatus disclosed in Non-Patent Document 1, a partial space within the magnetically shielding apparatus is covered with the high permeability magnetic body to enhance the magnetic shield effect of the partial space (Patent Document 2: JP-A No. 128193/1999). In addition, in Non-Patent Document 1 and Patent Documents 1, 2, the high permeability material is employed as the magnetically shielding technique. On the contrary, there has been reported a magnetically shielding apparatus using a superconducting cylinder that does not transmit a magnetism at all (Patent Document 3: JP-A No. 97696/1994).
In Patent Document 3, the superconducting cylinder that is open at both ends thereof is used, and both of those open ends are closed by superconducting plates, respectively. In the case where the superconductor is used as the magnetic shield material, it is necessary to make a superconducting state. As a result, there arise the following problems. Because a cooling mechanism is required, the device is prevented from being complicated increased in the size. Also, because the opening portions are closed, the entrance into and exit from the cylinder become troublesome, and a narrow closed space is provided.